A conventional backhoe mounted on an earth moving machine has an articulated boom that is pivotally mounted for swinging movement about a horizontal pivot means carried on a swing post coupled by a vertical pivot means to a frame structure of the earth moving machine. The raising and lowering movement of the boom and the side swinging movement of the swing post, and thereby of the boom, are actuated by hydraulic rams or cylinder mechanisms. During transport of the earth moving machine from one place to another, either under its own power or on a flatbed truck, the boom is hydraulically raised to prevent the earth digging bucket mounted on the free end of the boom from dragging on the ground. The swing post, and thereby the boom, are centered relative to the frame structure of the earth moving machine to avoid increasing the effective width of the earth moving machine or overhanging the sides of the flatbed truck on which the latter is being carried.
It has been found, however, that because of internal hydraulic oil leakage in the hydraulic position rams, the boom has a tendency to droop causing the bucket to drag on the ground or to drag on the truck bed or loading ramps as the machine is being moved on or off the truck bed.
Also, because of internal hydraulic oil leakage, the swing post has a tendency to permit the boom and its bucket to swing from side to side as the earth moving machine is driven down the road or is carried on the flatbed truck. This side to side swaying effect of the swing post and the boom, if permitted to attain any degree of magnitude, can result in steering instability of the earth moving machine or of the transporting vehicle.
Prior art patents, of which we are aware, have directed themselves primarily to the problem of maintaining the boom in a locked raised position. Devices limited to locking the boom in a raised position are disclosed in U.S. Pat. No. 3,811,582 issued May 21, 1974 to John F. Shumaker et al for a "Backhoe Boom Lock"; U.S. Pat. No. 3,921,835 issued Nov. 25, 1975 to Donald C. Baker et al for a "Releasable Lock Means for Boom"; and U.S. Pat. No. 3,995,761 issued Dec. 7, 1976 to Joseph C. Hurlburt for "Anti Lowering Device for a Boom Loader."
It is also known in the prior art, to use chains to restrict the movement of the boom and also of the swing post. In lieu of the chains, it is also known to use pins which may be inserted through aligned apertures in the boom and supporting frame structure to hold the boom in transport position. The difficulty with both the chains and the pins is that the loose sections of chain and the loose pins are frequently misplaced or deliberately not used. Frequently, the operator does not bother to lock the swing post and the boom when he has to move the earth moving machine only a few hundred meters from one place on the job to another, although the terrain over which he must traverse may be extremely rough. As a result, the operator finds his boom swinging from side to side and the bucket dragging on the ground, both of which can create steering instability that could result in an accident.
It is an object of the present invention to provide a boom locking means that is easily accessible to the operator from his station and which simultaneously mechanically locks the boom against lowering movement from a fully raised position and also the swing post and thereby the boom against swinging movement from side to side.